Back to Error DirectoryW3C EPUBCheck Standard
CSS-001Retailer Warning

The "resource" property must not be included in an EPUB Style Sheet.

The "resource" property must not be included in an EPUB Style Sheet.

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What This Error Means in Plain English

EPUBCheck detected The "resource" property must not be included in an EPUB Style Sheet.. Digital reading systems and bookstores require standard conformance to ensure compatibility across all reading apps.

Why Retailers & EAA Regulations Block This File

Automated book distributors (Apple Books, Amazon KDP, Kobo, and IngramSpark) run strict EPUBCheck validation on ingest and reject non-compliant files.

Technical Specification: W3C EPUBCheck rule CSS-001: The "resource" property must not be included in an EPUB Style Sheet.

Manual Fix Instructions (for Sigil / Calibre)

  1. Locate the file and line flagged under rule CSS-001 in your EPUB editor (Sigil or Calibre).
  2. Apply the required syntax correction matching the CSS-001 specification.
  3. Re-pack and validate with PreFlight EPUB to confirm zero residual errors.